Test with newer compilers in CI

Test with newer compilers in CI

Now compiles with clang 12 and gcc 11 without warnings in various
configurations. Did not update santizer configurations as they're
already on clang 11.

Adjusted various CI job intents to be either accurate or placed on
more suitable configurations.

Eliminated one build container, since we target only gcc versions that
are most recent supported, oldest supported, and if needed also those
required for e.g. support of most recent and oldest supported CUDA
versions.

Code changes mostly related to false positives.

Suppresses a false-positive warning in GoogleTest

Avoids warnings about loop variables referring to temporaries. Our
usage was safe, but the warning is potentially valuable elsewhere, so
we should respect it.

Rewrote a test with idiomatic value-parametrization to avoid a warning
about a reference to a temporary

Refs #3912